Belt grinding machine



Nov# 16, 1954 K. H. R. PETTE'RSSON 2,694,276

BELT GRINDING MACHINE Filed Nov`. 24, 1952 3 Sheets-Sheet 1 /fmvu- Hita/Ive @when 'Erre/frase. :By K

K. H. R. PETTERSSQN 2,694,276

BELT GRINDING MACHINE Filed Nov. 24, 1952 3 Sheets-Sheet 2 IIVVE/V TOI? Amw. HMP/NG '53m-MM 'Errewsofy Nov. 1e, 1954 K. H, R. PETTERSSON BELT GRINDING MACHINE Filed Nov. 24, 1952 5 Sheets-Sheet 5 UnitedStates Patent @dice 2,694,276 Patented Nov. 16, 1954 BELT GRINDING MACHINE Karl Hiiding Ragnar Pettersson, Halsngborg, Sweden Application November 24, 1952, Serial No. 322,216 Claims priority, application Sweden December 3, 1951 Claims. (Cl. 51--147) The present invention relates to belt grinding machines for grinding or polishilng objects by means of a belt running along a frame or arm between a drive pulley at one end of the arm and a grinding head forming a belt support at the other end of the arm.

The belt grinding machines hitherto known are constructed in such a way that the grinding belt runs approximately like a drive belt over a drive pulley and a number of return and tensioning pulleys in a common frame which is possibly also provided with a stationary or adjustable belt support behind the grinding belt at the grinding station. These machines are completely satisfactory for treating plane and cylindrical surfaces but their mobility is too limited for working bulging surfaces of a more complex or irregular form. lt is true that also the motor can be mounted on the frame and the whole machine can be handled as a manual tool, but this is possible only in case the grinding machine has small dimensions and small want of power, for in other cases the machine will be too diicult to handle,

The invention aims at an improvement in this respect implying that the machine is provided with a belt support which is more movable in relation to the drive pulley so that the heavy parts of the machine do not have to take part in all of its movements, but the belt support and consequently also the grinding belt can be tilted and turned in order to follow the more or less irregular surface which is to be worked.

A primary object with the present invention is to provide in a belt grinding machine such a driving means for the belt that part thereof can run slack and'so that the belt can be partly guided and supported by means slidingly engaged by the belt, thereby permitting the arm to be articulate without demands for additional guide pulleys.

Thus in one embodiment the invention provides a belt grinding machine comprising a base, a motor mounted on said base, a drive pulley mounted on said base and driven by said motor, an arm mounted on said base and extending radially in relation to said drive pulley and having an elbow joint and a swivel, a grinding head carried by the outer end of said arm and forming a belt support, a guide pulley on said arm at said joint, a grinding belt running about said drive pulle said guide pulley, and said belt support, the pulling run of said belt engaging said guide pulley and the idling run of said belt engaging the outer surface of said pulling run over said guide pulley, and a pinch pulley mounted adjacent said drive pulley and pinching said grinding belt thereagainst for driving it with its idling run slack.

If the belt is completely smooth, i. e. if it has no overlapping joints or similar irregularities, a stabilizing pulley for the idling run can be stationarily mounted in the frame and leave the belt untensioned to such a degree as to form a free loop between the drive pulley or the pinch pulley and the guide pulley. During operation, said loop is tensioned due to the kinetic energy of the belt, and the belt forms from the point where it leaves the drive pulley or the pinch pulley an S-shaped curve whose rst turn is completely free whereas the second turn engages the stabilizing pulley. The tension to which the free turn is subjected by centrifugal force is suiiicient for causing the belt to run steadily and smoothly throughout its length.

If the belt has an overlapping joint or if it has not approximately the same weight per unity of length throughout, the guiding described above may however become too slack, in which case the stabilizing pulley must be movably mounted and spring loaded so that it 'just keeps the belt straight.

In any case the belt -is caused to run steadily without the tensioning causing such a strong friction between the belt runs that the wear and loss of effect arising from said friction or the heat generated thereby having any decisive importance with regard to the practical use yof the machine. In that connexion it is possible to use to advantage the fact that a thin layer of air always ac companies the belt in its motion and that the tensioning of the idling run of the belt over the guide pulley is so weak that said air layer does not disappear altogether. Besides it will be of a certain importance that both runs move rapidly over the guide pulley and that each portion of the belt is thus subjected to friction for a very short moment only, during which it has hardly any time to give off any heat to the guide pulley and then has time to be cooled olf before passing the guide pulley next time.

Another object is to provide a belt grinding machine having a belt support for pressing the belt against the workpiece, which belt support can be profiled according o wish for working surfaces of a complex or irregular orm.

Other objects and advantages of the invention will be apparent from the following description of a preferred embodiment of the invention which is shown in the appended drawings.

Fig. l shows a complete belt grinding machine in elevation, whereas Fig. 2 shows, on a larger scale, part of the frame of the machine in the same projection as Fig. l and with a protective plate removed.

Fig. 3 is a side view of a grinding head embodied in accordance with the invention.k

Fig. 4 is a plan View of the grinding head shown in Fig. 3, and

Fig. 5 is a central longitudinal section thereof.

The frame of the machine shown consists of three relatively movable parts, viz. a base plate 1, a turntable 2, which is mounted on the base plate by means of a pivot 3 and on which there is mounted an electric motor with the shaft horizontal, and a frame in the form of an oblong ilat casing 4, which is pivotally mounted with one of its ends on the motor shaft 5 or concentrically therewith on the motor or the turntable, and a pair of rods 6 projecting from the other end of the casing, the outer ends of which rods are united with one another and carry a joint pin 7 parallel with the motor shaft.

The frame 4, 6 forms the inner portionv of the movable arm of the machine, an over arm below and a forearm. The movable arms 8 consists of a pair of rods united at their ends and mounted at one end on the joint pin 7, which thus forms an elbow joint, and carrying a swivel sleeve 9 at the other end. In said sleeve there is mounted a swivel pin 10 having at its outer end a pair of lugs 11 with a joint pin 12, and on said pin a second swivel sleeve 13 is mounted by means of a pair of lugs 14. In the last-mentioned swivel sleeve, finally, there is mounted a grinding head 15 around which the belt turns.

The grinding head 15 shown consists essentially of a sleeve 41 which is secured in the terminal swivel sleeve i3 of the movable arm 3 of the belt grinding machine and through which the grinding belt runs over a belt support 43 attached to the front portion of the sleeve, and then turns around the front end thereof and runs back through the sleeve and further to the drive pulley of the grinding machine, which pulley is so arranged, as will be described later, that that run of the belt which leaves said pulley does not have to be subjected toa greater tension then required in order that the belt may run steadily.

The belt support 43 consists of some laminae which are placed together so that their front ends form a rounded and, on the lower side, oblique support face for the back of the belt and are clamped vtogether and simultaneously clamped to a rigid plate 44 mounted on the sleeve, by means of a resilient clamp 45. The belt supportv projects some distance in front of the plate 44, so that when pressing the grinding belt against a workcasing l.

piece it can be bent somewhat, whereby the front ends of the laminae are displaced in relation to one another in the longitudinal direction of the block. The support face behind the belt can almost never become completely smooth but is as a rule stepped with transverse recesses at the contact surfaces between the laminae which form air inlets, and the result is that the grinding belt more or less floats on an air layer considerably reducing the heat-generating friction. It has turned out in practice that with such a belt support it is possible to work heavy steel objects so powerfully and continuously that the surfaces become blue-hot without the belt support being heated from room temperature to more than approximately 40 C.

Through the laminated construction` a further advantage is gained, viz. that the profile of the belt support can be changed at discretion by the various laminae being advanced more or less, and simultaneously its degree of resiliency can be regulated by the portion located in front of the stationary plate being made longer or shorter.

When the machine is not in use the over-arm 4, 6 is preferably directed straight upwards, and the fore-arm with the grinding head hangs down along the over-arm, the handle 15 being held fast by a spring clip 17 on the in order that the arm may automatically occupy this position it can be balanced to a suitable degree with respect to the motor shaft. lt can also be provided with some arresting means known per se, so that it can be comfortably adjusted and retained in the desired angle of inclination.

The grinding belt is driven by a drive pulley 21 mounted directly on the motor shaft 5, said pulley being enclosed in the lower portion of the casing 4 and pulling one run 22 of the belt from the guiding head 15 over two guide pulleys 23 and 24 which are mounted on the joint pins 12 and 7 respectively of the arm. ln order that the pulling force may then be suliicient without the other run of the belt having to be tensioned, a pinch pulley 2S is disposed adjacent the drive pulley in order to press the belt against said pulley. The pinch pulley is mounted on an arm 26 which is pivotally mounted at one end in the casing 4 and loaded at its other end by a spring 27 anchored in the casing.

On the shaft of the pinch pulley there is also mounted an arm 2S which is provided at its free end with a stablizing pulley 29 and which is loaded with a weak helical spring 3d anchored on the shaft of the pinch pulley in order to give the belt the very tension which is necessary in order to make it run smoothly. If the belt is suii'lciently smooth in itself the spring 30 can be dispensed with and the stabilizing pulley 29 can be fixed in such a position that the belt can leave the pinch pulley and form a free loop between said pulley and the stabilizing pulley, which is indicated in dash and dot lines at 29a in Fig. 2.

From the stabilizing pulley the idling portion 31 of the belt runs to the grinding head over the guide pulleys 24 and 23 outside of the pulling run 22, which, due to the insignificant tensioning, can take place without the friction becoming inadvantageously great.

At the joint between the fore-arm and the grinding head the guide pulley 23 is placed in such a way, through a suitable shape of the lugs 11 and 13, that the centre lines of the swivels form tangents thereto and so that the belt will run centrally through the swivels. This prevents any tendency to displace the belt laterally. At the joint between the over-arm and the fore-arm the guide pulley 24, is so desired, can be eccentrically mounted with respect to the joint pin 7, so that the belt is not tensioned or slackened to any considerable degree through the joint motion.

What I claim and desire to secure by Letters Patent 1s:

1. A belt grinding machine comprising a base, a motor mounted on said base, a drive pulley mounted on said base and driven by said motor, an arm mounted on said base and extending radially in relation to said drive pulley and having an elbow joint and a swivel, a grinding head carried by the outer end of said arm and forming a belt support, a guide pulley on said arm at said joint, a grinding belt running about said drive pulley, said guide pulley, and said belt support, the pulling run of said belt engaging said guide pulley and the idling run of said belt engaging the outer surface of said pulling run over said guide pulley, and a pinch pulley mounted adjacent said drive pulley and pinching said grinding belt thereagainst for driving it with its idling run slack.

2. A belt grinding machine having a drive pulley, drive means for said drive pulley, a grinding head forming a belt support, a grinding belt running about said drive pulley and said belt support, and a pinch pulley mounted adjacent said drive pulley and pinching said belt thereagainst for driving it with its idling run slack, said belt support consisting of a plurality of iiexible laminae placed on one another so that their ends form a support surface profiled at discretion for the back of said grinding belt and clamped together at a point spaced from said ends so that said laminae can yield under the grinding pressure, thereby being displaced longitudinally in relation to each other at said ends.

3. A belt grinding machine comprising a base, a turntable on the base, a motor mounted on the turntable with its shaft in a plane at right angles to the axis of the turntable, a drive pulley on the shaft of the motor, a frame pivotally connected at one end with the turntable for angular movement about the motor shaft, an arm member articulated by a joint at its inner end to the frame, a grinding head connected with the outer end of the arm member by a hinge joint and a swivel at either side of the hinge joint and forming a belt support, a guide pulley on the arm member at each joint, a grinding belt running about the drive pulley, the guide pulleys, and the belt support, thereby forming a pulling run and an idling run, the pulling run engaging the guide pullies and the idling run engaging the outer surface of the pulling run, and a pinch pulley mounted in the frame for co-operation with the drive pulley and loaded to pinch the grinding belt for driving it with the idling run slack.

4. A belt grinding machine according to claim 5, having a stabilizing member mounted in the frame and engaging the idling run of the grinding belt between the pinch pulley and the lirst guide pulley to make the slack of the belt run steadily.

5. A belt grinding machine as claimed in claim 5 having a stabilizing member movably mounted in the frame and engaging the idling run of the grinding belt between the pinch pulley and the lirst guide pulley, said stabilizing member being spring loaded to keep the slack of the belt straightened.

References Cited in the tile of this patent UNITED STATES PATENTS Number Name Date 296,535 Coy Apr. 8, 1884 1,798,421 Hitchcock Mar. 31, 1931 1,974,806 Curtis et al Sept. 25, 1934 1,999,275 Bertrand Apr. 30, 1935 2,313,254 Mead Mar. 9, 1943 2,470,615 Grover May 17, 1949 

